1. Technical Field
The present invention relates to a method for adapting a service provided by a base station in a cellular communication network as well as to a corresponding system.
2. Description of Related Art
Energy consumption and CO2 emissions have recently become topics of particular interest across the cellular telecommunication industry. Around 80% of the energy consumption and CO2 emissions from cellular network operators are originated within their networks and more specifically within the base stations thereof (wherein a base station in case of second generation GSM cellular networks is referred to as Base Transceiver Station/BTS and in case of third generation UMTS cellular networks is referred to as Node B). The overall contribution of cellular network operators to the excess of human CO2 emissions is estimated at 2%, see “Smart 2020: enabling the low carbon economy in the information age” GeSI, Global e-Sustainability Initiative. Hence reducing and optimising energy consumption of this particular element of the network is a strategic target for the cellular communication industry, not only because it makes business sense (around 10% of the network's operating expenses is budgeted for energy consumption in mature markets, this figure is significantly higher in emerging markets), but also companies are more and more engaged in Corporate Social Responsibility programs with particular focus on sustainability and environmental actions. The topic acquires particular relevance in emerging markets, with a poor or no electricity grid, and with a significant amount of base stations using diesel generators, which are particularly greedy in terms of operational expenditure, CO2 emissions & logistic requirements. Those off grid or poor grid diesel powered base stations are widespread in countries like India or on the African continent, which is a strong barrier for further deployment of cellular communication services in those countries.
The combination of above factors is moving the cellular communication industry to the introduction of renewable sources of energy, such as solar energy, wind energy and bio-energy for the energy supply to their networks. These solutions are environmentally friendly and technically proven, but when it comes to real implementation there are several drawbacks that limit their applicability:                The number and size of elements (solar panels, wind turbines) required to provide standard service is often large, sometimes beyond workable and practical installation levels.        Sun and wind are intrinsically instable sources of energy, forcing operators to deploy significant sets of back-up batteries able to supply the necessary energy during periods of shortage of sun, wind, etc.        
Regarding the dimensioning of renewable equipment, the following criteria are usual practice across the industry:                The renewable energy generator typically consists of solar panels or wind turbines. Sun or wind are inherently unstable energy sources that shall be able to provide, when working at maximum performance enough energy to feed the average power consumption needs of the BTS/Node B and also charge the batteries to face the next sun/wind outage. As a rule of thumb, the criterion used for dimensioning solar panels or other renewable energy generators is that a completely empty set of batteries shall be fully refilled during a period of ten days without outage of the renewable energy source, i.e. ten sunny days, ten windy days, etc. For determining the amount of solar panels to be installed or the turbine size to be used, not only the required generated energy should be taken into account but also the environmental conditions where the BTS/Node B is located.        During night time (in case of using solar panels as energy generator) or other outages (rainy periods, no wind periods, or in case that a hybrid energy supply is used with a diesel generator, no spare diesel), a battery back-up supply consisting of a set of batteries is utilized to provide energy to the base station during a back up period. A typical rule of thumb for base stations, which are only supplied with renewable energy sources, is that the batteries shall be able to carry the energy corresponding to the typical consumption of the base station over three days. So, the base station works normally in case of three consecutive days without supply of renewable energies, e.g. three days without sun, wind, etc.        
Furthermore, renewable energy generators can be used in combination with diesel generators or the grid in a hybrid mode, reducing the diesel consumption or the renewable infrastructure requirements. There are already several techniques available to minimize diesel consumption or optimize efficiency by means of a smart combination of working cycles and proper performance regimes.
The dimensioning criteria previously discussed are a usual practice across the industry, but they can be modified to ensure a higher service commitment or to relax the level of passive infrastructure needs. However, in the first case for most of the time the energy available for supply to the base station will be much higher than the energy consumption thereof, which is inefficient. In the second case, on the contrary, there will be a relatively long time without any service provided by the base station, because of lack of supplied energy.